1. Field of the Invention
The present invention relates to data processing apparatuses and data recording apparatuses, for recording image data, for example, into a tape-shaped recording medium and for reproducing the image data from the recording medium.
2. Description of the Related Art
As typically represented by a digital video cassette recorder (VCR), data recording and reproduction apparatuses for recording a digital image signal into a magnetic tape and for reproducing from the recording medium are known. In a recording processing section of a digital image recording unit, processing called shuffling for rearranging data in an order different from the original order is performed. Shuffling is performed for the following reasons.
Firstly, shuffling is performed to disperse a burst error due to a scratch on the tape in order to increase immunity against an error in an error correcting code (ECC) block. As the ECC, a product code is employed in many cases. The product code is obtained by applying external-code encoding to two-dimensional video data or audio data in the vertical direction and by applying internal-code encoding in the horizontal direction to encode the data symbols doubly. A data set formed of data, external-code parities, and internal-code parities is called an ECC block.
As shown in FIG. 17A, data in one ECC block is recorded into one track in a helical-scanning VCR. An extremely large number of errors may occur in the data in this track due to a head clog in the helical-scanning VCR as shown in FIG. 17B by shadows. In this case, the errors cannot be corrected with the error correcting capacity of the ECC and the whole ECC block data cannot be reproduced.
On the other hand, when data in one ECC block is shuffled and recorded in a plurality of tracks as shown in FIG. 18A, even if a burst error occurs in the whole track as shown in FIG. 18B, the burst error is dispersed by the processing (deshuffling) reverse to shuffling in reproduction processing and thereby the error is suppressed in one ECC block such that it can be corrected. Assuming that the direction of an internal code matches a recording and reproduction direction, a burst error is corrected by an external code at a high possibility.
Secondly, a shuffling operation is performed to allow a concealment process to be performed to make otherwise uncorrectable errors less conspicuous to the viewer. In other words, when error correcting fails, an interpolated image is generated with the use of spatial redundancy or time redundancy of an image in error conceal processing. The distribution of pixels which cannot be reproduced due to a burst error is controlled in shuffling to make a condition appropriate for concealing. With a combination of shuffling and concealing, a reproduced image is made easier to see when error correcting fails.
FIGS. 19A and 19B show a second advantage of shuffling. FIG. 19A shows a condition in which a loss of one track is dispersed on the screen by the use of shuffling. FIG. 19B shows a condition in which a loss of one track is collectively placed at a part of the screen by shuffling. One of these two types of shuffling is selected according to whether the data to be recorded is compressed data or non-compressed data. The condition shown in FIG. 19A is effective for non-compressed video data. The condition shown in FIG. 19B is effective for compressed video data. Effectiveness differs depending on whether an error concealing method uses surrounding correct pixels to interpolate an error pixel in the space domain or uses correct data in the preceding frame to interpolate an error pixel in the time domain.
Thirdly, shuffling is performed to make a reproduced image easier to see in a speed-change reproduction, in which a reproduction operation is performed at a tape speed different from that used in recording. Since the head scans a tape over a plurality of tracks in the speed-change reproduction, reproduced image data is fragmentarily collected from a plurality of tracks. Depending on a tape speed in a speed-change reproduction, image data which can be fragmentarily reproduced and image data which cannot be fragmentarily reproduced may be fixed in position on the screen. In this case, a part of the image is not updated in a speed-change reproduction, and thereby the contents of the reproduced image are difficult to understand. Shuffling can prevent this problem.
FIGS. 20A and 20B show a third advantage of shuffling. As shown in FIG. 20A, image data recorded into a part of a track is dispersed on the screen by shuffling. Conversely, image data recorded into a part of a track may be collectively placed at a portion on the screen as shown in FIG. 20B. In the same way as in the description of the second advantage of shuffling, which shuffling method is effective depends on a data condition, compressed or non-compressed. In other words, the method shown in FIG. 20A is effective for non-compressed video data. The method shown in FIG. 20B is effective for compressed video data.
As described above, shuffling is an effective method for improving reproduced-image quality when a tape-shaped recording medium is used. Which shuffling form (hereinafter called shuffling pattern) is employed is determined with all of an input-image format, the structure of an ECC block, and a recording format on a tape being taken into account. Conventionally, a shuffling pattern is represented by an appropriate expression and a calculation circuit for performing the processing of the expression is mounted.
In environments where digital broadcasting has been developed, a number of types of video and audio formats (each including a field frequency, the number of lines, interlaced scanning/progressive scanning, a screen size, and an aspect ratio) are used. Therefore, it is expected that a digital VCR handles a plurality of video and audio formats. In a conventional digital VCR, however, when an input-image format or a recording data rate is changed, a shuffling circuit for performing most appropriate shuffling is required to be designed again and mounted. The VCR lacks flexibility in handling a plurality of formats.
Accordingly, it is an object of the present invention to provide a data processing apparatus and a data recording apparatus which allow shuffling processing appropriate for each of a plurality of input-data formats to be performed.
The foregoing object is achieved in one aspect of the present invention through the provision of a data processing apparatus for rearranging digital information data in an order different from the original order, including a shuffling table memory for storing a shuffling table, for receiving positional information indicating the position of a data unit in an input-data sequence as an address, and for outputting converted positional information obtained by converting the positional information according to the shuffling table; and means for storing a shuffling table selected from a plurality of shuffling tables into the shuffling table memory.
The foregoing object is achieved in another aspect of the present invention through the provision of a data recording apparatus for rearranging digital information data in an order different from the original order and for recording the rearranged digital information data into a tape-shaped recording medium, including a data accumulation memory for accumulating digital information data; a shuffling table memory for storing a shuffling table, for receiving positional information indicating the position of a data unit in an input-data sequence as an address, and for outputting a write or read address of the data accumulation memory by converting the positional information according to the shuffling table; means for storing a shuffling table selected from a plurality of shuffling tables in the shuffling table memory; an error correcting encoder for applying error-correcting-code encoding to at least one of the input data and the output data of the data accumulation memory; and recording means for recording the data error-correcting encoded by the error correcting encoder into a tape-shaped recording medium.
One of a plurality of shuffling tables is selected according to the format of input digital information data (video data and/or audio data). Therefore, input digital information data having a plurality of formats can be shuffled. Since a shuffling pattern is provided as a table, shuffling more complicated than that represented by an expression can be provided, and thereby error immunity is improved. Successful error concealing is possible. In addition, image quality in speed-change reproduction can be improved.